In Dunedin this week, he said speculation that Mr Ryall would be changing a considerable number of board chairpersons reflected the problem the minister had with trusting people in important positions in the health sector.
Since Mr Ryall had been in power there had been massive erosion of capability in the Ministry of Health and the ministry's capacity to do its job had been greatly diminished.
Mr Hague said he was fearful of the same thing with wholesale change in the leadership of boards. He predicted huge loss of experience and knowledge from the sector, "to our cost".
He also expressed concern that throughout the country, Mr Ryall was directly phoning people in low levels of district health board management, something he described as "incredibly inadvisable".
Such "inappropriate" relationships meant that everyone "between the person phoned and the minister is unsure of their ground", and unsure whether they could get on with their job without the risk of being "second-guessed by the minister".
This could leave people scared to make decisions and lead to "paralysis by fear" in the sector, which was "the last thing we need".
Usually, health ministers' main contact was with the board chairpersons, although at times some things were discussed with chief executives, but usually with "chairmen kept in the loop".
"It is highly unusual for the minister to go below the level of chief executive. This minister has chosen to go quite a lot below that, not to talk about a broad overview, but to talk about quite detailed operational matters."
Mr Ryall's office, asked for comment on Mr Hague's concerns, said he would not be commenting on opposition speculation.
There has been increasing speculation that the Southern board will be chaired by Timaru accountant and former South Canterbury District Health Board chairman Joe Butterfield.
Asked about the place of chairing appointments outside of regions, Mr Hague said his experience of it on the West Coast had been a positive one, but someone from outside could have difficulty with the community aspect of the job.
While boards were legally accountable to the minister, they also felt an ethical accountability to their communities, which meant they walked a "tightrope".
Mr Ryall is expected to announce his board appointments before the end of the month.
